A huge number of studies, researches and investigations have heretofore been carried out on pyrimidine derivatives, leading to syntheses of a great number of compounds and finding of many compounds showing characteristic physiological activities in the fields of agricultural chemicals and pharmaceutical products. Many of these known pyrimidine derivatives were however prepared by substituting functional groups at the 2-, 4- and 6-positions of the pyrimidine skeltone, which functional groups are ready to undergo such substitution. The pyrimidine skeleton is much less reactive at its 5-position. There are only a few methods known to introduce a substituent group directly to the 5-position, all of which methods require to conduct nitration, halogenation or the like under certain specified conditions. Unless such known methods are followed, it is indispensable to employ an indirect method for the introduction of a desired substituent group, namely, to synthetically prepare a pyrimidine derivative from a compound which has in advance had the desired substituent group at a position corresponding to the 5-position of the resultant pyrimidine derivative.
As exemplary known pyrimidine derivatives having substituent groups at their 5-positions, may be mentioned as agricultural fungicides 5-n-butyl-2-dimethylamino-4-hydroxy-6-methylpyrimidine, 5-n-butyl-2-ethylamino-4-hydroxy-6-methylpyrimidine, etc. which are disclosed in British Patent Specification No. 1,182,584.
German Patent Offenlegungsschrift No. 2,341,925 discloses that the compounds represented by the general formula: ##STR2## wherein R.sup.1 is --NO.sub.2, Me, Et, Cl, --SCN, CO.sub.2 Et, Br, --CN, --SMe, F, p--ClC.sub.6 H.sub.4 S--, BuO-- or --CHO and R.sup.2 means a morpholino or piperidino group are useful as pharmaceutical products.
There are a relatively small number of compounds having a methylthio group as a substituent group attached to the 5-position. Except for the compounds described in the above-referred to specifications, there have been known only the following related compounds which are all disclosed in the Chemical Abstracts:
__________________________________________________________________________ --64, 15896h ##STR3## Pharmaceutical antibacterial chemical --72, 3499s ##STR4## Dye intermediate --72, 66891j ##STR5## Novel preparation process --73, 3832g ##STR6## Novel preparation process --76, 46212t ##STR7## Pharmaceutical product --78, 97696c ##STR8## R, R.sup.1 : amino groups; herbicide; fungicide --79, 137181k ##STR9## Pharmaceutical product --82, 156364f ##STR10## Pharmaceutical product --89, 101721d ##STR11## X,Y: Cl, alkylamino; herbicide --90, 54968y ##STR12## Herbicide __________________________________________________________________________
As illustrated above, substituent groups are bonded in many instances to the pyrimidine rings through nitrogen atoms in the above known 5-methylthiopyrimidine derivatives having substituent groups at their 2-, 4- and 6-positions. There have not been known to date any compounds which have, at all the 2-, 4- and 6-positions thereof, substituent groups bonded to the pyrimidine rings through oxygen or sulfur atoms.
The present inventors have synthetically obtained compounds having the above-mentioned structure, which compounds have never been synthesized so far, and tested their physiological effects, resulting in completion of this invention.